1. Field of the Invention
The present invention relates to a thermally assisted magnetic head having a semiconductor surface-emitting laser.
2. Related Background Art
Thin-film magnetic heads must deliver ever greater performance to cope with higher recording densities in hard disk drives. Widely used thin-film magnetic heads include composite thin-film magnetic heads having a multilayer structure comprising, for instance, a magnetic sensing element such as a magnetoresistive (MR) effect element and an electromagnetic coil element. These elements write and read data signals to/from a magnetic disk, which is a magnetic recording medium.
The magnetic recording medium is normally a so-called discontinuous medium having a structure in which magnetic microparticles are aggregated, each magnetic microparticle constituting a single domain structure. One recording bit comprises a plurality of magnetic microparticles. In order to enhance recording density, therefore, the magnetic microparticles must be made smaller, and the irregularities at the boundaries between recording bits must be reduced. Reducing the size of magnetic microparticles, however, is problematic in that reduction in particle volume is accompanied by a drop in magnetization thermal stability.
The factor KUV/kBT is an indicator of magnetization thermal stability. KU is the magnetic anisotropy energy of the magnetic microparticles, V is the volume of one magnetic microparticle, kB is the Boltzmann constant, and T is the absolute temperature. Making the magnetic microparticles smaller implies reducing their volume V. In turn, this makes KUV/kBT smaller, thereby impairing thermal stability. An approach for addressing this problem is increasing KU commensurately, but doing so results in a larger coercitivity of the recording medium. In contrast, the strength of the write magnetic field afforded by the magnetic head is largely determined by the saturation flux density of the soft magnetic material that makes up the magnetic poles in the head. Thus, writing may become impossible when the coercitivity exceeds a tolerance that is determined on the basis of the limits of the strength of the write magnetic field.
Proposed methods for solving the problem of magnetization thermal stability include using a magnetic material having a large KU, and resorting to so-called thermally assisted magnetic recording, in which writing is carried out by lowering coercitivity through heating of the recording medium immediately before application of a write magnetic field. Thermally assisted magnetic recording can be broadly classified into magnetic dominant recording and optical dominant recording. In magnetic dominant recording, writing is governed by an electromagnetic coil element, and the radiation diameter of light is larger than the track width (recording width). In optical dominant recording, on the other hand, writing is governed by a light-radiating section, and the radiation diameter of light is approximately equal to the track width (recording width). That is, magnetic field determines the spatial resolution in magnetic dominant recording, whereas light determines the spatial resolution in optical dominant recording.
U.S. Pat. No. 6,944,112 and Japanese Patent Application Laid-open No. 2005-317178 disclose hard disk drives comprising a thermally assisted magnetic head and a light source such as a semiconductor laser or the like. In the hard disk drive disclosed in U.S. Pat. No. 6,944,112, the light source is provided at a position spaced apart from the thermally assisted magnetic head. Emission light from this light source strikes an optical waveguide in the thermally assisted magnetic head, and is led through the optical waveguide to a near-field light generating section provided at a medium-facing surface. The magnetic recording medium is heated by near-field light generated by the near-field light generating section, to carry out thermally assisted magnetic recording.
In the hard disk drive disclosed in Japanese Patent Application Laid-open No. 2005-317178, a semiconductor laser as the light source and the thermally assisted magnetic head are formed integrally as a single unit. Thermally assisted magnetic recording is carried out by heating the magnetic recording medium through direct irradiation thereon of emission light from the light source.